Conventionally, as rollers which were employed in continuous molten zinc plating baths, continuous molten aluminum plating baths, or continuous molten zinc-aluminum plating baths, as well as members of molten plating accessory facilities onto which these molten metals are splattered, rollers made of heat-resistant steel, the surface of which is coated with various types of cermet system materials or oxide system ceramic materials, and which is then subjected to sealing treatment using a chromic acid system solution, a metal alkoxide alcohol solution, a colloidal silica solution, or the like, are employed, and have had some success.
However, when members are employed in which various types of cermet materials or oxide system ceramic materials are flame-coated onto the surface of a roller in a molten metal plating bath, and then conventional sealing treatment is carried out, when such members are employed in molten metal baths for a long period of time, there is intrusion of molten metal into the flame coating as a result of a decline in the corrosion resistance with respect to molten metal of sealing treatment itself, or there is intrusion of molten metal into the holes present in the flame coating, and thereby, erosion or alloying of the material parts of the members for use in molten metal baths occurs, and this is a cause of peeling of the flame coating.
Furthermore, when rollers for use in molten metal plating baths are employed which have sealing treatment executed by conventional flame-sprayed surface coatings, as a result of contact with the passing plate material (steel plate), the flame coating on the surface of the roller in the bath, which was subjected to sealing treatment, is likely to be abraded, so that the sealing effect decreases, and thereby, intrusion of the molten metal into the flame coating occurs, and this is also a cause of the peeling of the flame coating as described above.
It has been proposed, in Japanese Patent Application No HEI 9-122904, that as a means for solving this problem, an oxide ceramic flame coating in which a variety of oxides are combined be formed after flame coating a cermet material, comprising metal borides within a range of 5-60 weight percent, one or more of Co, Cr, Mo, or W in an amount within a range of 5-30 weight percent, the remainder comprising metal carbides and unavoidable impurities, onto the surface of a steel member, and conducting sealing treatment using an inorganic sealing agent on this composite coating. An example of the inorganic system sealing agent described here is a colloidal silica solution. With respect to this colloidal silica solution, in general, this is a solution comprising only a colloid of ultrafine granules of silicic acid having a grain diameter within a range of 1-100 nanometers. By means of this, there is a sealing effect; however, it is not sufficient, and concrete measures for improving the properties thereof have been desired.
The present invention solves the problems described above in the conventional technology; it has as an object thereof to provide a manufacturing method for members for use in molten metal baths, which have flame coatings having superior resistance to corrosion and resistance to peeling with respect to molten metal.